1. Field of the Invention
The invention relates to a hydraulic brake unit and a control method for the hydraulic brake unit.
2. Description of the Related Art
Typically, a conventional brake control apparatus electronically controls the supply and stoppage of oil pressure in a hydraulic system using an actuator to regulate oil pressure to be supplied to respective wheel cylinders. This type of brake control apparatus may include an accumulator serving as a power hydraulic pressure source, whereby the accumulator serves as a power source that operates the wheel cylinders together with oil pressure from a master cylinder unit corresponding to an operation of a brake pedal.
The brake control apparatus further includes a plurality of oil pressure sensors for performing appropriate control of the hydraulic system. By opening and closing a control valve provided in the hydraulic system on the basis of the oil pressure detected by the oil pressure sensors, thereby setting the hydraulic system in a communicative state or a blocked state, transmission supply and blocking of the oil pressure are controlled, and as a result, the oil pressure is supplied after being regulated to a desired value.
When a fault occurs in the hydraulic system such that brake fluid leaks out from the location of the fault, it may be difficult to maintain and generate the desired oil pressure. To avoid such faulty states to the greatest extent possible, thereby preventing the occurrence of a situation in which the hydraulic system cannot generate the desired oil pressure such that a braking operation is greatly impaired, various proposals have been made.
For example, in Japanese Patent Application Publication No. 2007-131247 (JP-A-2007-131247), a hydrobooster mode is used as a preliminary control mode employed when brake regeneration cooperative control is not performed due to a fault or the like. In the hydrobooster mode, a separation valve is closed such that a first system is separated from a second system. Hence, even when fluid leaks from a pipe, a braking force can be applied by the system in which the fluid leakage has not occurred.
Further, in Japanese Patent Application Publication No. 2006-264675 (JP-A-2006-264675), a part of a plurality of solenoid pressure reducing control valves provided between a plurality of brake cylinders and a low pressure source is used as a solenoid linear valve such that hydraulic pressures of the plurality of brake cylinders are controlled in common by controlling the pressure reducing solenoid linear valve. Then, on the basis of a relationship between hydraulic pressures detected by oil pressure sensors, a determination is made as to whether or not a leak has occurred.
However, in cases of hydraulic medium leakage, there remains room for improvement in terms of suppressing excessive decrease of the hydraulic medium due to the leak rapidly and reducing the effects thereof on a braking operation.